The present invention relates generally to blood glucose monitoring systems for determining the concentration of glucose in blood, and more particularly, to a sensor cartridge for dispensing biosensors for use with blood glucose monitoring systems.
It is often necessary to quickly obtain a sample of blood and perform an analysis of the blood sample. One example of a need for obtaining a sample of blood is in connection with a blood glucose monitoring system, which a user must frequently use to monitor the user's blood glucose level.
Those who have irregular blood glucose concentration levels are medically required to regularly self-monitor their blood glucose concentration level. An irregular blood glucose level can be brought on by a variety of reasons, including illness, such as diabetes. The purpose of monitoring the blood glucose concentration level is to determine the blood glucose concentration level and then to take corrective action, based upon whether the level is too high or too low, to bring the level back within a normal range. The failure to take corrective action can have serious implications. When blood glucose levels drop too low, a condition known as hypoglycemia, a person can become nervous, shaky and confused. That person's judgment may become impaired and that person may eventually pass out. A person can also become very ill if their blood glucose level becomes too high, a condition known as hyperglycemia. Both conditions, hypoglycemia and hyperglycemia, are potentially life-threatening emergencies.
One method of monitoring a person's blood glucose level is with a portable, hand-held blood glucose testing device. The portable nature of these devices enables the users to conveniently test their blood glucose levels wherever the user may be. The glucose testing device includes a biosensor to harvest the blood for analysis. One type of biosensor is the electrochemical biosensor. The electrochemical biosensor includes a regent designed to react with glucose in the blood to create an oxidation current at electrodes disposed within the electrochemical biosensor which is directly proportional to the user's blood glucose concentration. Such a biosensor is described in U.S. Pat. Nos. 5,120,420, 5,660,791, 5,759,364, and 5,798,031, each of which is incorporated herein in its entirety. Another type of sensor is an optical biosensor, which incorporates a reagent designed to produce a colorimetric reaction indicative of a user's blood glucose concentration level. The colorimetric reaction is then read by a spectrometer incorporated into the testing device. Such an optical biosensor is described in U.S. Pat. No. 5,194,393, which is incorporated herein by reference in its entirety.
In order to check a person's blood glucose level, a drop of blood is obtained from the person's fingertip using a lancing device, and the blood is harvested using the biosensor. The biosensor, which is inserted into a testing unit, is brought into contact with the blood drop. The biosensor draws the blood, via capillary action, inside the biosensor and the ensuing electrochemical reaction is measured by the test unit, which then determines the concentration of glucose in the blood. Once the results of the test are displayed on a display of the test unit, the biosensor is discarded. Each new test requires a new biosensor.
Referring now to FIGS. 1 and 2, examples of a testing device 10 and a package 30 of biosensors 12 (“sensor pack”) are shown, respectively. The sensor pack 30 is designed to be housed within the testing device 10. Prior to each test, a collection area 14 of an individual biosensor 12 is pushed by a mechanism within the testing device 10 through its packaging and is extended from the testing device 10 through a slot 16 for harvesting a sample of blood. The testing device 10 includes a slider 18 for advancing the biosensor 12. In FIG. 1, a biosensor 12 is shown extending from the testing device 10. The collection area 14 extends from the testing device 10, while a contact area, disposed at the opposite end of the biosensor 12, shown in FIGS. 1 and 2, remains inside the testing device 10. The contact area includes terminals that electrically couple the electrodes to a meter disposed within the testing device 10 for measuring the oxidation current produced at the electrodes by the reaction of glucose and the reagent. The test unit includes a display 20.
Referring now to FIG. 2, biosensors 12 are shown disposed in the sensor pack 30. The sensor pack 30 is made up of a circular disk 32 having ten individual compartments (blisters) 34 arranged radially. The disk is made from an aluminum foil/plastic laminate which is sealed to isolate the sensor from ambient humidity and from other sensors with a burst foil cover 36. Each biosensor 12 is kept dry by a desiccant located inside a desiccant compartment 37I disposed adjacent to the compartment 34.
To retrieve a sensor, a mechanism disposed within the testing device 10, such as a knife, is driven down through the burst foil into an individual elongated compartment 34 at the end closest to the hub of the disk 32 and then moved radially toward the perimeter of the blister 34. In doing so, the knife engages the contact area 38 (fish tail) of the sensor in that compartment. Radial travel of the knife pushes the tip of the sensor out through the burst foil 36 and through parts of the testing device 10 such that the collection area 14 of the sensor 12 is completely out of the testing device 10 and ready to receive a fluid test sample such as blood. For this stage, it is essential that the bond between the base and lid of the sensor withstand the sheer forces generated when the sensor bursts out through the foil 36. This method of providing a sensor ready for use is more fully described in U.S. Pat. No. 5,575,403, which is incorporated herein by reference in its entirety.
Further details of the operational and mechanical aspects of the testing device 10 and sensor pack 30 are more fully described in U.S. Pat. Nos. 5,575,403, 5,630,986, 5,738,244, 5,810,199, 5,854,074, 5,856,195 and 8,105,536, each of which are hereby incorporated by reference in their entireties.
A drawback associated with this flat array of testing devices is the large area that is occupied. The size of testing devices that internally house such a flat array package constrains the size of the package (i.e., the number of sensors), thus making it difficult to increase the number of sensors per package. Moreover, prior art meter and cartridge assemblies include too many parts that must be replaced with each new cartridge. Finally, sensors must be handled by the user, which decreases the accuracy of the reading. Accordingly, it would be beneficial to provide a replaceable cartridge where the replaceable portions are few and easily assembled to a meter, resulting in a lower cost of use and better accuracy in measurement.